This invention relates to a conveyor comprising a stationary mounted runway rail and a crab having load and guide wheels for conveying workpieces along the rail.
Conveying systems based on a wide variety of designs are used in many sectors of technology to convey goods which may take the form of individual parts or baskets for holding a plurality of such parts. For instance, it is known to use a frame having a runway rail and a crab for transporting mechanically or chemically treated parts which are often disposed in bins or baskets. The unsupported length of the runway rail must span the total distance of conveyance. The crab has a hoist for raising and lowering the workpieces.
Conveyors of this kind usually have a runway rail of rectangular cross-section on which a crab is disposed for longitudinal motion by means of load and guide wheels extending from the crab. Conveyors of this kind are disclosed, for instance, in German patent application DE-OS Nos. 27 18 640 and 27 09 208.
Conveyors of the known type have significant disadvantages. The cross-section of the material used for the rail must be dimensioned by taking into account both the load to be carried and the length to be spanned. Consequently, the runway rail may be oversized when the loads to be carried are relatively light or the lengths to be spanned are relatively short. Also, as shown in German OS No. 27 09 208 it is known to utilize a series of individual rail portions, one after another in a unit type construction, for providing conveyor distances of different lengths. A disadvantage of this latter construction resides in the fact that each individual portion must have a cross-section suitable for the maximum length and the maximum load.
Rectangular cross-sections of the known conveyors fail to provide accurate guidance for the crab. Accurate crab motions in the direction along the rail and transversely thereof are essential when microprocessors are used for controlling such motions as is the case, for instance, in ultrasonic cleaning installations.
The crab must be positioned accurately for this particular use. In known conveyors, such as can be seen in German OS No. 23 43 502, the crab is driven by means of a load wheel friction drive. This kind of drive is not suited for accurate positioning. Other friction drives are known which use drive belts, for instance German OS No. 26 45 883. Friction drives are used frequently when abrupt and jerky changes of motion are to be avoided. Clearly, a crab cannot be accurately positioned by means of the above stated drives unless further adjustment means are provided.
It is a principal object of this invention to provide a conveyor which can be adapted economically to required loadings and spans.
Another important object of this invention is the provision of a conveyor system in which the crab motion is controlled with a high degree of precision.
Other objects and advantages of the present invention will become more clearly apparent by reading the following description in conjunction with the accompanying drawings.